Spent nuclear reactor fuel is a huge problem for power companies and state and local governments. The storage of spent nuclear reactor fuel poses threats and security risks. Efforts and regulations have focused on the safe storage of spent nuclear reactor fuel in secret and hardened facilities. Early storage efforts placed spent nuclear fuel assemblies and rods in pools located in hardened and secret buildings. More recently, spent nuclear reactor fuel dry storage casks have been developed to secure and store spent nuclear reactor fuel assemblies. The casks are hardened to withstand bomb strikes and terrorist threats. The casks include passive cooling fins to dissipate heat generated by the decay of the spent nuclear reactor fuel, and are also structured to contain radiation generated by the decay. The casks may be stored in the open, or in buildings, or underground locations that may include additional external cooling to aid heat dissipation. The focus of all efforts to store and secure spent nuclear fuel has been safe containment of the fuel to prevent accidental or deliberate radiation releases and structures have been designed with this in mind to withstand both attacks and catastrophes. No emphasis has yet been placed on designs intended to realize, benefits from the such stored spent nuclear fuel.
In the United States, there are 103 commercial nuclear reactors that generate about 20% of the total electrical energy used in the United States each year, which is about 3% of the total energy used in the United States each year. The average age of these reactors is in excess of 25 years and the typical reactor undergoes a complete fuel change-out about every 3-4 years with the used (spent) fuel elements (assemblies) typically being stored on site in spent fuel storage pools protected by secret locations and hardened buildings. This represents a great deal of spent nuclear reactor fuel. The addition of nuclear capacity in the United States remains possible as efforts seek to reduce dependency of the nation's energy supply upon fossil fuels. Increase in nuclear power capacity will further increase the amount of spent fuel storage required.
The Nuclear Waste Policy Act (NWPA; as amended) stipulates that the federal government (DOE) will take title to the spent fuel from these reactors and will place it into permanent geological storage at the Yucca Mountain site in Nevada. Even with the enabling legislation for this disposal in place and the needed funds ($22B) having been collected as a surcharge on nuclear electricity sales over the years, still Congress has refused to actually appropriate the funds to implement the geological disposal in Yucca Mountain as is required by the NWPA. Thus, spent fuel assemblies have continued to accumulate in spent fuel storage pools at the various reactor sites around the US to the point that the storage pools at many sites are filled to capacity.
Transferring ownership of spent fuel and the physical transporting of spent fuel are either not allowed under the current NWPA or are subject to intense public/political opposition. This has led utilities to implement alternative storage options for spent fuel such as the dry cask storage cask. These casks are quite large, to accommodate the unprocessed size of spent fuel assemblies. The outer portion of the cask is in the range of 20-30 feet in height with a diameter of about 10 feet. The outer portion encloses an inner canister, and a bundle of spent fuel assemblies is within the inner canister. Shielding protects against emissions from the case, and fan systems are used to cool the cases.
Spent fuel assemblies consist of about 95% unburned enriched uranium, plutonium, and other transuranic species (all potential future fuels) and about 5% isotope species and their decay byproducts (some very scarce and industrially valuable). The isotopes in spent fuel include species that decay very rapidly (hours or days), species that decay with medium rapidity (10's to 100's of years), and species that decay very slowly (1000's to millions of years). Following removal from a reactor and about 1 year spent cooling off in the spent fuel storage pool, a spent fuel assembly can have enough radioactivity still present to result in the generation of heat equivalent to about 0.1% of its operational power while still in the reactor. Thus, a typical spent fuel assembly from a Westinghouse PWR such as the Callaway Plant in Fulton, Missouri will still be producing thermal power of roughly 150-200 kiloWatts from the radioactive decays of the isotopes and transuranic species after 1 year of storage. At present, this energy is simply dissipated via passive and active cooling to maintain safety of the spent nuclear reactor fuel.
Spent nuclear fuel is not presently reprocessed in the U.S. Reprocessing plants have been previously build in the U.S., but various regulations and test failures long ago caused U.S. plants to be shut down. Reprocessing is conducted in other countries. Various products can be obtained by reprocessing spent fuel, but these depend upon the fuel, its initial enrichment, and the time the fuel has been used. As an example, reprocessed U-238 will normally have less than 1% U-235 (typically about 0.5% U-235) and also smaller amounts of U-232 and U-236 created in the reactor. The U-232 has daughter nuclides which are strong gamma-emitters. The primary idea behind present reprocessing efforts is to repurpose the reprocessed fuel to be used again as part of a re-enriched fuel source in a nuclear reactor. Generally, spent fuel of a reactor is processed to obtain a concentrated metal oxide. The concentrated oxide generally includes, as a small percentage of an array of other elements, including both isotopes and actinides formed in the reactor. Further processing can obtain isolate specific isotopes.